U.S. patent application number 10/618665 was filed with the patent office on 2004-01-29 for ceramic heater.
This patent application is currently assigned to IBIDEN CO., LTD.. Invention is credited to Furukawa, Masakazu, Hiramatsu, Yasuji, Ito, Yasutakaq.
Application Number | 20040016746 10/618665 |
Document ID | / |
Family ID | 30448972 |
Filed Date | 2004-01-29 |
United States Patent
Application |
20040016746 |
Kind Code |
A1 |
Ito, Yasutakaq ; et
al. |
January 29, 2004 |
Ceramic heater
Abstract
An objective of the present invention is to provide a ceramic
heater making it possible to heat an object to be heated, such as a
silicon wafer, uniformly. The ceramic heater of the present
invention is a ceramic heater wherein a heating element is formed
on a surface of a ceramic plate or inside the ceramic plate,
wherein: a bottomed hole is made, being directed from the opposite
side to a heating surface for heating an object to be heated,
toward the heating surface; the bottom of said bottomed hole is
formed relatively nearer to the heating surface than the heating
element; and a temperature-measuring element is set up in this
bottomed hole.
Inventors: |
Ito, Yasutakaq; (Ibi-gun,
JP) ; Furukawa, Masakazu; (Ibi-gun, JP) ;
Hiramatsu, Yasuji; (Ibi-gun, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
IBIDEN CO., LTD.
1 Kandacho 2-chome Ogaki-shi
Gifu
JP
503-0917
|
Family ID: |
30448972 |
Appl. No.: |
10/618665 |
Filed: |
July 15, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10618665 |
Jul 15, 2003 |
|
|
|
09926092 |
Dec 27, 2001 |
|
|
|
09926092 |
Dec 27, 2001 |
|
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PCT/JP00/08154 |
Nov 20, 2000 |
|
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Current U.S.
Class: |
219/444.1 ;
118/725 |
Current CPC
Class: |
H05B 1/0233 20130101;
H05B 3/265 20130101; H05B 3/283 20130101; H05B 3/143 20130101; H01L
21/67248 20130101 |
Class at
Publication: |
219/444.1 ;
118/725 |
International
Class: |
H05B 003/68 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 29, 1999 |
JP |
11/377206 |
Jan 4, 2000 |
JP |
2000-000149 |
Claims
1. A ceramic heater comprising a ceramic plate and a heating
element formed on a surface of said ceramic plate or inside
thereof, wherein: a bottomed hole is made, being directed from the
opposite side to a heating surface for heating an object to be
heated, toward the heating surface; the bottom of said bottomed
hole is formed relatively nearer to the heating surface than the
heating element; and a temperature-measuring element is set up in
said bottomed hole.
2. The ceramic heater according to claim 1, wherein the distance
between the bottom of said bottomed hole and said heating surface
is from 0.1 mm to 1/2 of the thickness of the ceramic plate.
3. The ceramic heater according to claim 1, wherein the ceramic
constituting said ceramic heater is a nitride ceramic or a carbide
ceramic.
4. The ceramic heater according to claim 1, wherein said heating
element is divided into at least two circuits.
5. The ceramic heater according to claim 1, wherein said heating
element has a section in a flat shape.
6. A ceramic heater comprising a ceramic plate and a heating
element formed on a surface of said ceramic plate or inside
thereof, said ceramic heater being equipped with: a
temperature-measuring element for measuring the temperature of said
ceramic plate; a control unit for supplying electric power to said
heating element; a memory unit for memorizing the data of a
temperature measured by said temperature-measuring element; and an
operation unit for calculating electric power required for said
heating element from said temperature data, wherein: a bottomed
hole is made, being directed from the opposite side to a heating
surface for heating an object to be heated, toward the heating
surface; the bottom of said bottomed hole is formed relatively
nearer to the heating surface than the heating element; and a
temperature-measuring element is set up in said bottomed hole.
7. The ceramic heater according to claim 6, wherein said heating
element is divided into at least two circuits and different
electric powers are supplied to the respective circuits.
8. The ceramic heater according to any of claims 1 to 7, wherein
said temperature-measuring element is a sheath type
thermocouple.
9. The ceramic heater according to any of claims 1 to 8, wherein
said temperature-measuring element is pressed on the bottom portion
of the bottomed hole.
10. The ceramic heater according to claim 9, wherein said
temperature-measuring element is pressed thereon, by means of an
elastic body or a screw.
11. The ceramic heater according to any of claims 1 to 10, wherein
said temperature-measuring element is sealed in the bottomed hole
with an insulator.
Description
TECHNICAL FIELD
[0001] The present invention relates to a ceramic heater for
drying, sputtering or the like, used mainly in the semiconductor
industry, and particularly to a ceramic heater wherein the
temperature thereof can easily be controlled and the temperature
uniformity of its heating surface is superior.
BACKGROUND ART
[0002] A semiconductor product is produced through the steps of
forming a photosensitive resin as an etching resist on a silicon
wafer and subjecting the silicon wafer to etching, and the like
steps.
[0003] This photosensitive resin is liquid, and is applied onto a
surface of the silicon wafer, using a spin coater or the like.
After the application, the resin must be dried. Thus, the silicon
wafer subjected to the application process is put on a heater and
heated.
[0004] Hitherto, as a heater made of metal and used for such a
purpose, a heater wherein heating elements are arranged on the back
surface of an aluminum plate is adopted.
[0005] However, such a heater made of metal has the following
problems.
[0006] First, the thickness of the heater plate must be as thick as
about 15 mm since the heater is made of metal. This is because a
bend, a strain and so on are generated due to thermal expansion
resulting from heating so that a silicon wafer put on the metal
plate is damaged or inclined in case of a metal plate being thin.
However, if the thickness of the heater plate is made thick, the
heater becomes heavy and bulky.
[0007] Also, heating temperature is controlled by changing the
voltage or amperage applied to the heating elements. However, since
the metal plate is thick, the temperature of the heater plate does
not follow the change in the voltage or amperage promptly. Thus,
such a problem that the temperature cannot be easily controlled is
caused.
[0008] Thus, as suggested in JP Kokai Hei 8-8247, there is a
technique suggested, wherein a nitride ceramic on which heating
elements are formed is used to perform temperature-control while
measuring the temperature near the heating elements.
SUMMARY OF THE INVENTION
[0009] However, when such a technique is used to heat a silicon
wafer, a problem that the silicon wafer is damaged by thermal shock
resulting from a temperature-difference on the surface of the
heater is caused.
[0010] Thus, the inventors made eager investigations on causes of
the damage of the silicon wafer. As a result, the inventors have
found out that the occurrence of the damage of the silicon wafer,
in spite of performing temperature-control, is owing to the
following unexpected fact: when the temperature near the heating
elements is measured, the measured temperature is not necessarily
reflects the temperature of the heating surface for the silicon
wafer, therefore, a temperature-difference is generated in some
places of the silicon wafer and, thus the silicon wafer is
damaged.
[0011] The inventors have also found out a new fact that such
non-uniformity of the temperature is significant in ceramics having
a high thermal conductivity, such as nitride ceramic and carbide
ceramic.
[0012] Thus, repeating further investigations, the inventors have
found out that by measuring the temperature of a portion nearer to
the silicon wafer and heating the silicon wafer on the basis of the
thus obtained result, a temperature-difference on the heating
surface for the silicon wafer can be made small so that the ceramic
plate can be prevented from being damaged, and have made the
present invention which has, as the subject matter thereof, the
following contents.
[0013] That is, a ceramic heater of the first aspect of the present
invention is a ceramic heater comprising a ceramic plate and a
heating element formed on a surface of the ceramic plate or inside
thereof,
[0014] wherein:
[0015] a bottomed hole is made, being directed from the opposite
side to a heating surface for heating an object to be heated,
toward the heating surface;
[0016] the bottom of the bottomed hole is formed relatively nearer
to the heating surface than the heating element;
[0017] and a temperature-measuring element is set up in this
bottomed hole.
[0018] In the above-mentioned ceramic heater, the distance between
the bottom of the bottomed hole and the heating surface is
desirably from 0.1 mm to 1/2 of the thickness of the ceramic
plate.
[0019] The ceramic constituting the ceramic heater is desirably a
nitride ceramic or a carbide ceramic.
[0020] The heating element of the ceramic heater is desirably
divided into at least two circuits.
[0021] The heating element of the ceramic heater desirably has a
section in a flat shape.
[0022] A ceramic heater of the second aspect of the present
invention is a ceramic heater comprising a ceramic plate and a
heating element formed on a surface of the ceramic plate or inside
thereof, the ceramic heater being equipped with:
[0023] a temperature-measuring element for measuring the
temperature of the ceramic plate;
[0024] a control unit for supplying electric power to the heating
element;
[0025] a memory unit for memorizing the data of a temperature
measured by the temperature-measuring element; and
[0026] an operation unit for calculating electric power required
for the heating element from the temperature data,
[0027] wherein:
[0028] a bottomed hole is made, being directed from the opposite
side to a heating surface for heating an object to be heated,
toward the heating surface;
[0029] the bottom of the bottomed hole is formed relatively nearer
to the heating surface than the heating element;
[0030] and a temperature-measuring element is set up in this
bottomed hole.
[0031] It is desired that in the ceramic heater, the heating
element is divided into at least two circuits and different
electric powers are supplied to the respective circuits.
[0032] It is desired that in the ceramic heaters according to the
first and second of aspects of the present invention, the
temperature-measuring element is a sheath type thermocouple, and is
pressed on the bottom portion of the bottomed hole.
[0033] It is also desired that the temperature-measuring element is
pressed thereon, by means of an elastic body or a screw.
[0034] It is also desired that the temperature-measuring element is
sealed in the bottomed hole with an insulator.
BRIEF DESCRIPTION OF DRAWINGS
[0035] FIG. 1 is a bottom surface view that schematically shows an
example of a ceramic heater of the first aspect of the present
invention.
[0036] FIG. 2(a) is a block figure that schematically shows an
example of a ceramic heater of the second aspect of the present
invention, and FIG. 2(b) is a partially enlarged sectional view of
this ceramic heater.
[0037] FIG. 3 is a block figure that schematically shows another
example of a ceramic heater of the second aspect of the present
invention.
[0038] FIG. 4(a) is a sectional view that schematically shows an
example of a ceramic heater wherein a temperature-measuring element
is set up, and FIG. 4(b) is an enlarged bottom surface view showing
the shape of a bottomed hole.
[0039] FIG. 5(a) is a sectional view that schematically shows
another example of the ceramic heater wherein a
temperature-measuring element is set up, and FIG. 5(b) is an
enlarged bottom surface view showing the shape of a bottomed
hole.
[0040] FIG. 6 is a graph showing temperature profiles of a ceramic
heater according to Example 4.
[0041] FIG. 7 is a graph showing electric power profiles of a
ceramic heater according to Example 4.
EXPLANATIONS OF SYMBOLS
[0042]
1 10, 20, 40 a ceramic heater 11, 21, 41, 61, 71 a heater plate 12,
22, 42, 62, 72 a heating element 13, 23, 43 a terminal pin 14, 24,
44 a bottomed hole 15, 25, 45 a through hole 19 a silicon wafer
21a, 41a a heating surface 21b, 41b a bottom surface 26, 46 a
supporting pin 27, 47, 67 a thermocouple. 28 a conductor filled
through hole 29, 49 a control unit 30, 50 a memory unit 31, 51 an
operation unit 66 a cylinder 610, 710 a bottomed hole
DISCLOSURE OF THE INVENTION
[0043] The ceramic heater of the first aspect of the present
invention is a ceramic heater comprising a ceramic plate and a
heating element formed on a surface of the ceramic plate or inside
thereof,
[0044] wherein:
[0045] a bottomed hole is made, being directed from the opposite
side to a heating surface for heating an object to be heated,
toward the heating surface;
[0046] the bottom of the bottomed hole is formed relatively nearer
to the heating surface than the heating element;
[0047] and a temperature-measuring element is set up in this
bottomed hole.
[0048] According to the ceramic heater of the first aspect of the
present invention, a place for temperature-measurement is nearer to
a heating surface for an object to be heated (a silicon wafer) than
the heating element. Therefore, the temperature of the object to be
heated can be more correctly measured. By adjusting the heating
condition of the heating element on the basis of this measured
result of the temperature, the object to be heated can be uniformly
heated.
[0049] A nitride ceramic or a carbide ceramic has a smaller thermal
expansion coefficient than metals and a far higher mechanical
strength than metals. Thus, even if a ceramic plate (referred to as
a heater plate hereinafter) is made thin, the heater plate is not
warped or distorted by heating. As a result, the heater plate can
be made thin and light. Since the thermal conductivity of the
heater plate is high and the heater plate itself is thin, the
surface temperature of the heater plate follows a change in the
temperature of the heating element promptly. In other words, by
changing voltage or amperage to change the temperature of the
heating element, the surface temperature of the heater plate can be
controlled.
[0050] It is desired: that in the ceramic heater, the heating
element is formed on a surface which is one main face of the heater
plate and the opposite face is made to be a heating surface for
heating an object to be heated, such as a silicon wafer; or that
the heating element is formed, to be biased from the center toward
the side of one main face inside the heater plate and the surface
farther from the heating element is made to be a heating
surface.
[0051] By setting the position where the heating element is formed
in this way, heat generated from the heating element diffuses all
over the heater plate while the heat is conducted. As a result, the
temperature distribution in the surface for heating an object to be
heated (a silicon wafer) is made uniform so that the temperatures
in respective portions of the object are made uniform.
[0052] The heating is performed by putting the object to be heated
onto the heater plate, or by holding the object at a given distance
apart from the heater plate.
[0053] FIG. 1 is a bottom surface view that schematically shows an
example of a ceramic heater of the first aspect of the present
invention.
[0054] A heater plate 11 is formed into a disc form. Heating
elements 12 are formed into a pattern of concentric circles on the
bottom surface of the heater plate 11 in order to heat a heating
surface (an opposite face of the illustrated bottom surface) of the
heater plate 11 in such a manner that the temperature in the whole
of the heating surface thereof becomes uniform. As to these heating
elements 12, two concentric circles near to each other, as one set,
are connected into one line. Terminal pins 13, which will be
input/output terminals, are connected to two ends thereof. Through
holes 15 into which supporting pins (not illustrated) are inserted
are formed in areas near the center. Bottomed holes 14a to 14i into
which temperature-measuring elements are inserted are also
formed.
[0055] In the ceramic heater 10, the thickness of the heater plate
11 is preferably 0.5 to 5 mm. If the thickness is thinner than 0.5
mm, the strength thereof is lowered so that the heater plate is
easily damaged. On the other hand, if the thickness is thicker than
5 mm, heat is not easily conducted so that heating efficiency is
lowered.
[0056] The ceramic constituting the ceramic heater 10 is desirably
a nitride ceramic or a carbide ceramic.
[0057] Examples of the nitride ceramic include aluminum nitride,
silicon nitride, boron nitride and titanium nitride. These may be
used alone or in combination of two or more.
[0058] Examples of the carbide ceramic include silicon carbide,
zirconium carbide, titanium carbide, tantalum carbide and tungsten
carbide. These may be used alone or in combination of two or
more.
[0059] Among these, aluminum nitride is most preferred. The reasons
for this are as follows: its thermal conductivity is highest, that
is, 180 W/m.multidot.K and aluminum nitride has superior
temperature-following property, on the other hand, since aluminum
nitride easily causes non-uniformity of temperature distribution,
it is necessary to adopt the structure wherein the
temperature-measuring element is formed as is in the present
invention.
[0060] In the ceramic heater 10 of the first aspect of the present
invention, the distance L (reference to FIG. 2(b)) between the
bottom of the bottomed holes 14a to 14i and the heating surface is
desirably from 0.1 mm to 1/2 of the thickness of the ceramic plate.
If the distance between the bottom of the bottomed holes 14a to 14i
and the heating surface is below 0.1 mm, heat is radiated so that a
temperature distribution is produced on the heating surface for a
silicon wafer. On the other hand, if the distance is over 1/2 of
the thickness of the ceramic plate, the influence of the
temperature of the heating elements over the control apt to be
significant so that a temperature distribution is produced on the
heating surface for the silicon wafer.
[0061] Examples of the temperature-measuring element include a
thermocouple and a platinum temperature-measuring resistance, and a
thermistor.
[0062] Examples of the thermocouple include K, R, B, S, E, J and T
type thermocouples, as described in JIS-C-1602 (1980). Among these,
the K type thermocouple is preferred.
[0063] Desirably, the size of the connecting portion of the
thermocouple is equal to or more than the diameter of its strand
wire, and is 0.5 mm or less. If the connecting portion is large,
the thermal capacity is large so that the response becomes poor.
Incidentally, making the size smaller than the diameter of the
strand wire is difficult.
[0064] The diameter of the bottomed holes 14a to 14i is desirably
0.3 to 0.5 mm. If the diameter is too large, the heat radiant
property becomes too large. If the diameter is too small, the
processability becomes poor so that the distance between the
processing surface and the holes cannot be made uniform.
[0065] As shown in FIG. 1, the bottomed holes 14a to 14i are
desirably arranged into a cross form, and symmetrically with
respect to the center of the heater plate 11. Such arrangement
makes it possible to measure the temperature in the whole of the
heating surface.
[0066] The temperature-measuring elements may be bonded to the
bottoms of the bottomed holes 14a to 14i, using gold solder, silver
solder and the like. The temperature-measuring elements may be
inserted into the bottomed holes 14a to 14i and then the holes may
be sealed with an insulator such as a heat resistant resin or a
ceramic. The both manners may be used together.
[0067] Examples of the heat resistant resin may be thermosetting
resins, in particular, epoxy, polyimide, bismaleimide-triazine and
silicone resins. These resins may be used alone or in combination
of two or more. The sealing may be performed using a ceramic such
as silica sol or alumina sol.
[0068] The gold solver is desirably at least one selected from an
alloy of 37 to 80.5% by weight of Au-63 to 19.5% by weight of Cu,
an alloy of 81.5 to 82.5% by weight of Au-18.5 to 17.5% by weight
of Ni. These have a melting temperature of 900.degree. C. or higher
and are not easily melted even at a high temperature range.
[0069] The silver solder that can be used may be, for example, a
Ag-Cu type.
[0070] As shown in FIG. 1, the heating elements 12 are desirably
divided into at least two circuits, and more desirably divided into
2 to 10 circuits. By the division into the circuits, each electric
power supplied to the respective circuits can be controlled to
change the calorific value thereof so that the temperature of the
heating surface for a silicon wafer can be adjusted.
[0071] FIGS. 4, 5 are views each of which shows a method for fixing
a temperature-measuring element. FIGS. 4(a),5(a) are sectional
views each of which shows the vicinity of a bottomed hole. FIGS.
4(b),5(b) are enlarged bottom surface views each of which shows a
shape of the bottomed hole.
[0072] As shown in FIG. 4, when the temperature-measuring element
is fixed, the temperature-measuring element may be pressed on the
bottom surface of a bottomed hole 610, using an elastic body such
as a coil spring 65. As shown in FIG. 5, the temperature-measuring
element may be pressed against the bottom surface of a bottomed
hole 710, using a bolt 74. As the elastic body, the coil spring, a
plate spring and the like may be used.
[0073] When the temperature-measuring element is fixed with a
resin, a ceramic, a solder material or the like, it is apprehended
that such a material will deteriorate thermally so that the
temperature-measuring element may fall away. However, in the case
that a physical method such as pressing is used, such a problem is
not caused. Thus, such a case is favorable. As shown in FIGS. 4,5,
in the case that fixing based on pressing or the like is performed
and a thermocouple is used as the temperature-measuring element, it
is desired to use a sheath type thermocouple wherein the
thermocouple is inserted into a cylinder and the surrounding of the
thermocouple is filled with insulating powder such as alumina
powder. This is because: the structure of this type makes it
possible to prevent the thermocouple from being damaged.
[0074] Examples of the pattern of the heating elements 12 include
the concentric circuits shown in FIG. 1, a spiral, eccentrics, and
curved lines.
[0075] In the case that the heating elements 12 are formed on the
surface of the heater plate 11 in the present invention, adopting
the following method is preferred: a method of applying a conductor
containing paste containing metal particles to the surface of the
heater plate 11 to form a conductor containing paste layer having a
given pattern, and firing this to sinter the metal particles on the
surface of the heater plate 11. When: the metal particles are
melted and adhered to each other; and the metal particles and the
ceramic are melted and adhered to each other upon the sintering of
the metal, the sintering is sufficient.
[0076] When the heating elements 12 are formed on the surface of
the heater plate 11 as shown in FIG. 1, the thickness of the
resistance heating elements 12 is preferably 1 to 30 .mu.m and more
preferably 1 to 10 .mu.m. When the heating elements are formed
inside the heater plate 11, the thickness thereof is preferably 1
to 50 .mu.m.
[0077] When the heating elements 12 are formed on the surface of
the heater plate 11, the width of the heating elements is
preferably 0.1 to 20 mm and more preferably 0.1 to 5 mm. When the
heating elements are formed inside the heater plate 11, the width
of the heating elements is preferably 5 to 20 .mu.m.
[0078] The resistance value of the heating elements 12 can be
changed dependently on their width or thickness. The
above-mentioned ranges are however most practical. The resistance
value becomes larger as the heating elements become thinner and
narrower. The thickness and the width of the heating elements 12
become larger in the case that the heating elements 12 are formed
inside the heater plate 11. The reason for this is as follows:
[0079] when the heating elements 12 are formed inside, the distance
between the heating surface and the heating elements becomes short
so that the uniformity of the temperature on the surface becomes
poor, thus, it is necessary to make the width of the heating
elements 12 themselves large;
[0080] also, when the heating elements are formed inside, it is
unnecessary to consider the adhesiveness to any ceramic, for
example, a nitride ceramic. Therefore, it is possible to use a high
melting point metal such as tungsten or molybdenum, or a carbide of
tungsten, molybdenum and the like. Thus, it becomes possible to
make the resistance value thereof high. Therefore, the thickness
itself may be made large in order to prevent disconnection and so
on.
[0081] For these reasons, the heating elements 12 desirably have
the above-mentioned thickness and width.
[0082] The heating elements 12 may have a rectangular section or an
elliptical section. They desirably have a flat section. This is
because: in case of the flat section, heat is more easily radiated
toward the heating surface. Thus, a temperature distribution on the
heating surface is not easily generated.
[0083] The aspect ratio (the width of the heating element/the
thickness of the heating element) of the section is desirably 10 to
5000.
[0084] Adjustment thereof into this range makes it possible to
increase the resistance value of the heating elements 12 and keep
the uniformity of the temperature on the heating surface.
[0085] In the case that the thickness of the heating elements 12 is
made constant: if the aspect ratio is smaller than the
above-mentioned range, the amount of heat conduction toward the
wafer-heating surface of the heater plate 11 becomes small so that
a thermal distribution similar to the pattern of the heating
elements 12 is generated on the heating surface; on the other hand,
if the aspect ratio is too large, the temperature of the portions
just above the centers of the heating elements 12 becomes high so
that a thermal distribution similar to the pattern of the heating
elements 12 is also generated on the heating surface. Accordingly,
if temperature distribution is considered, the aspect ratio of the
section is preferably 10 to 5000.
[0086] When the heating elements 12 are formed on the surface of
the heater plate 11, the aspect ratio is desirably 10 to 200. When
the heating elements 12 are formed inside the heater plate 11, the
aspect ratio is desirably 200 to 5000.
[0087] The aspect ratio becomes larger in the case that the heating
elements 12 are formed inside the heater plate 11. This is based on
the following reason. If the heating elements 12 are formed inside,
the distance between the heating surface and the heating elements
12 becomes short so that temperature uniformity in the surface
becomes poor. It is therefore necessary to make the heating
elements 12 themselves flat.
[0088] The position where the heating elements 12 are formed to be
biased inside the heater plate 11 is desirably at a position near
the opposite face side(bottom surface) to the heating surface of
the heater plate 11 and at a position exceeds 50% and up to 99% of
the distance from a heating surface to the bottom surface.
[0089] If the value is 50% or less, the position is too near to the
heating surface so that temperature-dispersion is caused.
Conversely, if the value is over 99%, the heater plate 11 itself
warps to damage a silicon wafer.
[0090] In the case that the heating elements 12 are arranged inside
the heater plate 11, plural heating element formed layers may be
formed. In this case, the patterns of the respective layers are
preferably disposed in mutually complementary relation so that,
when viewed from above the heating surface, the patterns is formed
in all areas. A preferred example of such a structure having a
staggered arrangement.
[0091] The conductor containing paste is not particularly limited,
and is preferably a paste comprising not only metal particles or a
conductive ceramic for keeping electrical conductivity but also a
resin, a solvent, a thickener and so on.
[0092] The metal particles are preferably of, for example, a noble
metal (gold, silver, platinum or palladium), lead, tungsten,
molybdenum, nickel or the like. These may be used alone or in
combination of two or more. These metals are not relatively easily
oxidized, and have an resistance value sufficient for generating
heat.
[0093] Examples of the conductive ceramic include carbides of
tungsten and molybdenum, for example. These may be used alone or in
combination of two or more.
[0094] The particle diameter of these metal particles or the
conductive ceramic is preferably 0.1 to 100 .mu.m. If the particle
diameter is too fine, that is, below 0.1 .mu.m, they are easily
oxidized. On the other hand, if the particle diameter is over 100
.mu.m, they are not easily sintered so that the resistance value
becomes large.
[0095] The shape of the metal particles may be spherical or scaly.
When these metal particles are used, they may be a mixture of
spherical particles and scaly particles.
[0096] In the case that the metal particles are scaly or a mixture
of spherical particles and scaly particles, metal-oxides between
the metal particles are easily retained and adhesiveness between
the heating elements 12 and, for example, the nitride ceramic or
the like is made sure. Moreover, the resistance value can be made
large. Thus, this case is profitable.
[0097] Examples of the resin used in the conductor containing paste
include epoxy resins and phenol resins. An example of the solvent
is isopropyl alcohol. An example of the thickener is cellulose.
[0098] It is desired to add a metal oxide to the metal particles in
the conductor containing paste and make the heating element 12 into
a sintered body of the metal particles and the metal oxide, as
described above. By sintering the metal oxide together with the
metal particles in this way, the nitride ceramic or the carbide
ceramic, which is the heater plate, can be closely adhered to the
metal particles.
[0099] The reason why the adhesiveness to the nitride ceramic or
the carbide ceramic is improved by mixing the metal oxide is
unclear, but would be based on the following. The surface of the
metal particles, or the surface of the nitride ceramic or the
carbide ceramic is slightly oxidized so that an oxidized film is
formed thereon. Pieces of these oxidized films are sintered and
integrated with each other through the metal oxide so that the
metal particles and the nitride ceramic or the carbide ceramic are
closely adhered to each other.
[0100] A preferred example of the metal oxide is at least one
selected from the group consisting of lead oxide, zinc oxide,
silica, boron oxide (B.sub.2O.sub.3), alumina, yttria, and
titania.
[0101] These oxides make it possible to improve adhesiveness
between the metal particles and the nitride ceramic or the carbide
ceramic without increasing the resistance value of the heating
elements 12.
[0102] When the total amount of the above mentioned metal oxides is
set to 100 parts by weight, the weight ratio of the above mentioned
lead oxide, zinc oxide, silica, boron oxide (B.sub.2O.sub.3),
alumina, yttria and titania is as follows: lead oxide: 1 to 10,
silica: 1 to 30, boron oxide: 5 to 50, zinc oxide: 20 to 70,
alumina: 1 to 10, yttria: 1 to 50 and titania: 1 to 50. The weight
ratio is preferably adjusted within the scope that the total
thereof is not over 100 parts by weight.
[0103] By adjusting the amounts of these oxides within these
ranges, the adhesiveness to the nitride ceramic can be particularly
improved.
[0104] The addition amount of the metal oxides to the metal
particles is preferably 0.1% by weight or more and less than 10% by
weight. The area resistivity when the conductor containing paste
having such a structure is used to form the heating elements 12 is
preferably from 1 m.OMEGA./.quadrature. to 10
.OMEGA./.quadrature..
[0105] In the case that the heating elements 12 are formed on the
surface of the heater plate 11, a metal covering layer (reference
to FIG. 3) 48 is preferably formed on the surface of the heating
elements 12. The metal covering layer prevents a change in the
resistance value owing to the oxidization of the inner metal
sintered body. The thickness of the formed metal covering layer is
preferably from 0.1 to 10 .mu.m.
[0106] This is because: the metal used for forming the metal
covering layer is not particularly limited if the metal is a metal
which is hardly oxidized. Specific examples thereof include gold,
silver, palladium, platinum, and nickel. These may be used alone or
in combination of two or more. Among these metals, nickel is
preferred.
[0107] This is because: in the heating element 12, a terminal for
connecting to a power source is necessary. This terminal is fixed
to the heating element 12 through solder. Nickel prevents solder
from being thermally diffused. An example of the connecting
terminal is a terminal pin 13 made of koval.
[0108] In the case that the heating elements 12 are formed inside
the heater plate 11, no coating is necessary since the surface of
the heating elements is not oxidized. In the case that the heating
elements 12 are formed inside the heater plate 11, a part of the
heating elements may be exposed in the surface. It is allowable
that conductor filled through holes for connecting to the heating
elements are made in portions for the terminals and terminals are
connected and fixed to the conductor filled through holes.
[0109] In the case that the connecting terminals are connected, an
alloy such as silver-lead, lead-tin or bismuth-tin can be used as a
solder. The thickness of the solder layer is desirably from 0.1 to
50 .mu.m. This is because this range is a range sufficient for
maintaining connection based on the solder.
[0110] Electrodes may be embedded in the ceramic plate in the
ceramic heater of the present invention so that the ceramic heater
can function as an electrostatic chuck. In another case, a chuck
top conductor layer is deposited on the surface of the ceramic
heater and a guard electrode and a ground electrode may be formed
therein so that the ceramic heater can function as a wafer
prober.
[0111] The following will describe the process for producing a
ceramic heater wherein the heating elements 12 are formed on the
surface of the heater plate 11 shown in FIG. 1.
[0112] (1) Step of forming the heater plate
[0113] If necessary, a sintering aid such as yttria, a binder and
so on are blended with powder of a nitride ceramic, such as the
above-mentioned aluminum nitride, or a carbide ceramic to prepare a
slurry. Thereafter, this slurry is made into a granular form by
spray drying or the like. The granule is put into a mold and
pressed to be formed into a plate form or the like form. Thus, a
raw formed body(green) is formed.
[0114] Next, portions that will be the through holes 15 into which
supporting pins for supporting a silicon wafer are inserted, and
portions that will be the bottomed holes 14a to 14i in which
temperature-measuring elements such as thermocouples are buried;
are formed in the raw formed body by drilling, blast treatment or
the like if necessary.
[0115] Next, this raw formed body is heated and fired to be
sintered. Thus, a plate made of the ceramic is produced.
Thereafter, the plate is made into a given shape to produce the
heater plate 11. The shape of the raw formed body may be such a
shape that the sintered body can be used as it is. By heating and
firing the raw formed body under pressure, the heater plate 11
having no pores can be produced. It is sufficient that the heating
and the firing are performed at sintering temperature or higher.
The firing temperature is 1000 to 2500.degree. C. for nitride
ceramics or carbide ceramics.
[0116] (2) Step of printing a conductor containing paste on the
heater plate
[0117] A conductor containing paste is generally a fluid comprising
metal particles, a resin and a solvent, and has a high viscosity.
This conductor containing paste is printed in portions where
heating elements are to be arranged, by screen printing or the
like, to form a conductor containing paste layer. Since it is
necessary that the heating elements make the temperature of the
whole of the heater plate uniform, the conductor containing paste
is desirably printed into a pattern comprising concentric circles,
as shown in FIG. 1.
[0118] The conductor containing paste layer is desirably formed in
the manner that a section of the heating elements 12 after the
firing is rectangular and flat.
[0119] (3) Firing of the conductor containing paste
[0120] The conductor containing paste layer printed on the bottom
surface of the, heater plate 11 is heated and fired to remove the
resin and the solvent and sinter the metal particles. Thus, the
metal particles are baked onto the bottom surface of the heater
plate 11 to form the heating elements 12. The heating and firing
temperature is preferably 500 to 1000.degree. C.
[0121] If the above-mentioned metal oxides are added to the
conductor containing paste, the metal particles, the heater plate
and the metal oxides are sintered to be integrated with each other.
Thus, the adhesiveness between the heating elements and the heater
plate is improved.
[0122] (4) Step of forming a metal covering layer
[0123] A metal covering layer is desirably deposited on the surface
of the heating elements 12. The metal covering layer can be formed
by electroplating, electroless plating, sputtering or the like.
From the viewpoint of mass-productivity, electroless plating is
optimal.
[0124] (5) Fitting of terminals and so on
[0125] Terminals (terminal pins 13) for connecting to a power
source are fitted up to ends of the pattern of the heating elements
12 with solder. Thermocouples are fixed to the bottomed holes 14a
to 14i with silver solder, gold solder or the like. The bottomed
holes are sealed with a heat resistant resin such as a polyimide to
finish the manufacture of the ceramic heater 10.
[0126] The following will describe a process for producing a
ceramic heater wherein heating elements are formed inside a heater
plate.
[0127] (1) Step of forming the heater plate
[0128] First, powder of a nitride ceramic or a carbide ceramic is
mixed with a binder, a solvent and so on to prepare a paste. This
is used to form a green sheet.
[0129] As the above-mentioned ceramic powder, aluminum nitride,
silicon carbide or the like can be used. If necessary, a sintering
aid such as yttria may be added.
[0130] As the binder, desirable is at least one selected from an
acrylic binder, ethylcellulose, butylcellusolve, and polyvinyl
alcohol.
[0131] As the solvent, desirable is at least one selected from
.alpha.-terpineol and glycol.
[0132] A paste obtained by mixing these is formed into a sheet form
by the doctor blade process, to form a green sheet.
[0133] The thickness of the green sheet is preferably 0.1 to 5
mm.
[0134] Next, the following are made in the resultant green sheet if
necessary: portions which will be through holes into which
supporting pins for supporting a silicon wafer are inserted;
portions which will be bottomed holes in which
temperature-measuring elements such as thermocouples are buried;
portions which will be conductor filled through holes for
connecting the heating elements to external terminal pins; and so
on. After a green sheet lamination that will be described later is
formed, the above-mentioned processing may be performed.
[0135] (2) Step of printing a conductor containing paste on the
green sheet
[0136] A metal paste or a conductor containing paste containing a
conductive ceramic is printed on the green sheet.
[0137] This conductor containing paste contains metal particles or
conductive ceramic particles.
[0138] The average particle diameter of tungsten particles or
molybdenum particles is preferably 0.1 to 5 .mu.m. If the average
particle is below 0.1 .mu.m or over 5 .mu.m, the conductor
containing paste is not easily printed.
[0139] Such a conductor containing paste may be a composition
(paste) obtained by mixing, for example, 85 to 87 parts by weight
of the metal particles or the conductive ceramic particles; 1.5 to
10 parts by weight of at least one kind of binder selected from
acrylic binders, ethylcellulose, butylcellusolve and polyvinyl
alcohol; and 1.5 to 10 parts by weight of at least one solvent
selected from .alpha.-terpineol and glycol.
[0140] (3) Step of laminating the green sheets
[0141] Green sheets on which no conductor containing paste is
printed are laminated on the upper and lower sides of the green
sheet on which the conductor containing paste is printed.
[0142] At this time, the number of the green sheet laminated on the
upper side is made larger than that of the green sheet laminated on
the lower side to cause the position where the heating elements are
formed to be biased toward the bottom surface.
[0143] Specifically, the number of the green sheets laminated on
the upper side is preferably 20 to 50, and that of the green sheets
laminated on the lower side is preferably 5 to 20.
[0144] (4) Step of firing the green sheet lamination
[0145] The green sheet lamination is heated and pressed to sinter
the ceramic particles and the inner conductor containing paste in
the green sheets.
[0146] The heating temperature is preferably 1000 to 2000.degree.
C., and the pressing pressure is preferably 100 to 200 kg/cm.sup.2.
The heating is performed in the atmosphere of an inert gas. As the
inert gas, argon, nitrogen or the like can be used.
[0147] After the firing, bottomed holes into which
temperature-measuring elements will be inserted may be made. The
bottomed holes can be made by blast treatment such as sandblast
after surface-polishing. Terminals are connected to the conductor
filled through holes for connecting to the inner heating elements,
and then the resultant is heated for reflowing. The heating
temperature is suitably 200 to 500.degree. C.
[0148] Furthermore, thermocouples or the like as
temperature-measuring elements are inserted and set up with silver
solder, gold solder or the like, and then the holes are sealed with
a heat-resistant resin such as polyimide to finish the manufacture
of the ceramic heater.
[0149] The following will describe a ceramic heater of the second
aspect of the present invention.
[0150] The ceramic heater of the second aspect of the present
invention is a ceramic heater comprising a ceramic plate and a
heating element formed on a surface of the ceramic plate or inside
thereof, the ceramic heater being equipped with:
[0151] a temperature-measuring element for measuring the
temperature of the ceramic plate;
[0152] a control unit for supplying electric power to the heating
element;
[0153] a memory unit for memorizing the data of a temperature
measured by the temperature-measuring element; and
[0154] an operation unit for calculating electric power required
for the heating element from the temperature data,
[0155] wherein:
[0156] a bottomed hole is made, being directed from the opposite
side to a heating surface for heating an object to be heated,
toward the heating surface;
[0157] the bottom of the bottomed hole is formed relatively nearer
to the heating surface than the heating element;
[0158] and a temperature-measuring element is set up in this
bottomed hole.
[0159] According to the ceramic heater of the second aspect of the
present invention, a place for a temperature-measurement is nearer
to a heating surface for a silicon wafer than the heating element.
Therefore, the temperature of the silicon wafer can be more
correctly measured. This correctly measured result of the
temperature is memorized in the memory unit, and then an electric
power which is going to be supplied to the heating element in order
to perform uniform heating is calculated in the operation unit on
the basis of the temperature data memorized in the memory unit. On
the basis of the calculated result, a voltage for control is
applied to the heating element by the control unit. Therefore, the
whole of the silicon wafer can be uniformly heated.
[0160] A nitride ceramic or a carbide ceramic has a smaller thermal
expansion coefficient than metals and a far higher mechanical
strength than metals. As a result, the heater plate can be made
thin and light. Since the thermal conductivity of the heater plate
is high and the heater plate itself is thin, the surface
temperature of the heater plate follows a change in the temperature
of the heating element promptly.
[0161] FIG. 2(a) is a block figure that schematically shows an
example of a ceramic heater of the second aspect of the present
invention, and FIG. 2(b) is a partially enlarged sectional view
showing a part thereof.
[0162] As shown in FIG. 2, in this ceramic heater 20, plural
through holes 25 (only one in the figure) are made in a heater
plate 21. Supporting pins 26 are inserted into the through holes
25. A silicon wafer 19 is put on the supporting pins 26. By moving
the supporting pins 26 upwards or downwards, the silicon wafer 19
can be delivered to a non-illustrated carrier machine, or the
silicon wafer 19 can be received from the carrier machine.
[0163] By the supporting pins 26, the silicon wafer 19 can be held
at a given distance apart from the heater plate 21 and can be
heated.
[0164] Heating elements 22a and 22b are embedded in the heater
plate 21, and the heating elements 22a and 22b are connected,
through conductor filled through holes 28, to terminal pins 23
arranged on the bottom surface. The terminal pins 23 are fitted
with sockets 32, and the sockets 32 are connected to a control unit
29 having a power source.
[0165] Bottomed holes 24 are made, from the side of the bottom
surface 21b, in the heater plate 21. Thermocouples 27 are fixed to
the bottoms of the bottomed holes 24. The thermocouples 27 are
connected to a memory unit 30 so that the temperatures of the
respective thermocouples 27 are measured every given interval.
Thus, the data can be memorized. This memory unit 30 is connected
to a control unit 29 and an operation unit 31. On the basis of the
data memorized in the memory unit 30, the operation unit 31
calculates a voltage value and so on which are used for the
control. On the basis of this calculation, a certain voltage is
applied from the control unit 29 to the respective heating elements
21 so that the temperature on a heating surface 21a can be made
uniform.
[0166] Respective members (the heater plate 21, the heating
elements 22a and 22b, conductor filled through holes 28)
constituting the ceramic heater 20, bottomed holes 24 formed in the
heater plate 21, and so on are made in the same manner as in the
case of the ceramic heater of the first aspect of the present
invention. Thus, explanation thereof is omitted herein.
[0167] The following will describe the operation of the ceramic
heater 20 of the second aspect of the present invention.
[0168] First, the control unit 29 is operated so that an electric
power is supplied to the ceramic heater 20. As a result, the
temperature of the heater plate 21 itself rises, but the surface
temperature of the periphery thereof becomes slightly low.
[0169] The data measured by the thermocouples 27 are once stored in
the memory unit 30. Next, the temperature data are sent to the
operation unit 31. In the operation unit 31,
temperature-differences .DELTA.T among respective measured points
are calculated and further data .DELTA.W necessary for making the
temperature on the heating surface 21a uniform are calculated.
[0170] For example, in the case that the temperature-difference
.DELTA.T is generated between the heating element 22a and the
heating element 22b and the temperature of the heating element 22a
is lower, operations to obtain electric power data .DELTA.W for
making the .DELTA.T to zero are run, this data is transmitted to
the control unit 29 and an electric power based on this data is
supplied to the heating element 22a to raise the temperature
thereof.
[0171] Regarding the algorithm for calculating the electric power,
a method for calculating the electric power necessary for the rise
in the temperature by utilizing the specific heat of the heater
plate 21 and the weight of the heated area is most simple. A
correction coefficient originating from the pattern of the heating
elements may be considered together with these factors.
Alternatively, a temperature-rising test is beforehand performed on
a specific heating element pattern, and functions among a
temperature-measuring position, a supplying electric power and
temperature are beforehand obtained. From these functions, the
supplying electric power may be calculated. The applying voltage
and time corresponding to the electric power calculated in the
operation unit 31 are transmitted to the control unit 29. On the
basis of these values, electric powers are supplied to the
respective heating elements 22 by the control unit 29.
[0172] FIG. 3 is a block figure that schematically shows another
example of a ceramic heater of the second aspect of the present
invention.
[0173] In a ceramic heater 40 shown in FIG. 3, heating elements 42a
and 42b are formed on a bottom surface 41b of a heater plate 41,
and metal covering layers 48 are formed around the heating elements
42a and 42b.
[0174] A terminal pin 43 is connected and fixed to each of the
heating elements 42a and 42b through the metal covering layer 48.
The terminal pin 43 is fitted with a socket 52. This socket 52 is
connected to a control unit 29 having a power source. Other
elements are formed in the same way as in the ceramic heater shown
in FIG. 2.
[0175] The ceramic heater 40 shown in FIG. 3 operates in the same
way as the ceramic heater 20 shown in FIG. 2. The temperatures of
thermocouples 42a and 42b are measured every given interval. Thus,
the data is memorized in the memory unit 50. From the data, a
voltage value and so on for control are calculated in the operation
unit 51. On the basis of these, a certain amount of voltage is
applied from the control unit 49 to the heating elements 42a, 42b
so that the temperature in the whole of the heating surface 41a of
the ceramic heater 40 can be made uniform.
BEST MODE FOR CARRYING OUT THE INVENTION
[0176] The present invention will be described in more detailed
hereinafter.
EXAMPLE 1
Manufacture of a Ceramic Heater Made of Aluminum Nitride (Reference
to FIG. 1)
[0177] (1) A composition made of 100 parts by weight of aluminum
nitride powder (average particle diameter: 1.1 .mu.m), 4 parts by
weight of yttria (average particle diameter: 0.4 .mu.m), 12 parts
by weight of an acrylic binder and an alcohol was subjected to
spray-drying to make granular powder.
[0178] (2) Next, this granular powder was put into a mold and
formed into a flat plate form to obtain a raw formed body (green).
This raw formed body was drilled to form: portions which would be
through holes 15, into which supporting pins for the silicon wafer
are inserted; and portions (diameter: 1.1 mm, and depth: 2 mm)
which would be bottomed holes 14a to 14i, in which thermocouples
are buried.
[0179] (3) The raw formed body subjected to the above-mentioned
working treatment was hot-pressed at 1800.degree. C. and a pressure
of 200 kg/cm.sup.2 to obtain a nitride aluminum plate having a
thickness of 3 mm.
[0180] Next, this plate was cut out into a disk having a diameter
of 210 mm to obtain a plate (heater plate) 11 made of the
ceramic.
[0181] (4) A conductor containing paste was printed on the heater
plate 11 obtained in the step (3) by screen printing. The pattern
of the printing was made to a pattern of concentric circles as
shown in FIG. 1.
[0182] The conductor containing paste was Solvest PS603D made by
Tokuriki Kagaku Kenkyu-zyo, which is used to form plated through
holes in printed circuit boards.
[0183] This conductor containing paste was a silver-lead paste and
containing 7.5 parts by weight of metal oxides comprising lead
oxide (5% by weight), zinc oxide (55% by weight), silica (10% by
weight), boron oxide (25% by weight) and alumina (5% by weight) per
100 parts by weight of silver. The silver particles had an average
particle diameter of 4.5 .mu.m, and were scaly.
[0184] (5) Next, the heater plate 11 on which the conductor
containing paste was printed was heated and fired at 780.degree. C.
to sinter silver and lead in the conductor containing paste and
bake them onto the heater plate 11. Thus, heating elements 12 were
formed. The silver-lead heating elements 12 had a thickness of 5
.mu.m, a width of 2.4 mm and a area resistivity of 7.7
m.OMEGA./.quadrature..
[0185] (6) The heater plate 11 formed in the step (5) was immersed
into an electroless nickel plating bath comprising an aqueous
solution containing 80 g/L of nickel sulfate, 24 g/L of sodium
hypophosphite, 12 g/L of sodium acetate, 8 g/L of boric acid, and 6
g/L of ammonium chloride to precipitate a metal covering layer
(nickel layer) having a thickness of 1 .mu.m on the surface of the
silver-lead heating elements 12.
[0186] (7) A silver-lead solder paste (made by Tanaka Kikinzoku
Kogyo CO.) was printed by screen printing on portions to which
terminal for attaining connection to a power source were attached,
to form a solder layer.
[0187] Next, terminal pins 13 made of koval were put on the solder
layer and heated at 420.degree. C. for reflowing to attach the
terminal pins 13 onto the surface of the heating elements 12.
[0188] (8) Thermocouples for temperature-control were connected
with a gold solder of 81.7Au-18.3Ni (heated at 1030.degree. C. and
fused), to obtain a ceramic heater 10.
EXAMPLE 2
Manufacture of a Ceramic Heater Made of Silicon Carbide
[0189] A ceramic heater made of silicon carbide was manufactured in
the same way as in Example 1 except that silicon carbide having an
average particle diameter of 1.0 .mu.m was used, sintering
temperature was set to 1900.degree. C., and the surface of the
resultant heater plate was fired at 1500.degree. C. for 2 hours to
form a SiO.sub.2 layer having a thickness of 1 .mu.m on the
surface. The thermocouples were sealed by curing a polyimide resin
at 120.degree. C.
EXAMPLE 3
Manufacture of a Ceramic Heater Having Heating Elements Inside
Thereof
[0190] (1) A paste obtained by mixing 100 parts by weight of
aluminum nitride powder (made by Tokuyama Corp., average particle
diameter: 1.1 .mu.m), 4 parts by weight of yttria (average particle
diameter: 0.4 .mu.m), 11.5 parts by weight of an acrylic binder,
0.5 part by weight of a dispersant, and 53 parts by weight of
alcohols comprising 1-butanol and ethanol was formed into a green
sheet having a thickness of 0.47 .mu.m by the doctor blade
process.
[0191] (2) Next, this green sheet was dried at 80.degree. C. for 5
hours, and was subjected to punching to make portions which would
be through holes 15 having diameters of 1.8 mm, 3.0 mm and 5.0 mm,
respectively, into which silicon wafer supporting pins are
inserted, and portions which would be conductor filled through
holes for connection to terminal pins.
[0192] (3) 100 parts by weight of tungsten carbide particles having
an average particle diameter of 1 .mu.m, 3.0 parts by weight of an
acrylic binder, 3.5 parts by weight of .alpha.-terpineol solvent,
and 0.3 part by weight of a dispersant were mixed to prepare a
conductor containing paste A.
[0193] 100 parts by weight of tungsten particles having an average
particle diameter of 3 .mu.m, 1.9 parts by weight of an acrylic
binder, 3.7 parts by weight of .alpha.-terpineol solvent, and 0.2
part by weight of a dispersant were mixed to prepare a conductor
containing paste B.
[0194] The conductor containing paste A was printed on the green
sheet by screen printing, to form a conductor containing paste
layer. The printed pattern was made to a pattern of concentric
circles as shown in FIG. 1. The conductor containing paste B was
filled into the through holes which would be conductor filled
through holes for connection to terminal pins.
[0195] Thirty seven green sheets on which no tungsten paste was
printed were stacked on the upper side (heating surface) of the
green sheet subjected to the above-mentioned treatment, and 13
green sheets on which no tungsten paste was printed were stacked on
the lower side thereof, and then the green sheets were laminated at
130.degree. C. and a pressure of 80 kg/cm.sup.2.
[0196] (4) Next, the resultant lamination was degreased at
600.degree. C. in nitrogen gas for 5 hours, and hot-pressed at
1890.degree. C. and a pressure of 150 kg/cm.sup.2 for 3 hours to
obtain an aluminum nitride plate 3 mm in thickness. This was cut
out into a disc of 230 mm in diameter to prepare a ceramic heater
having therein heating elements having a thickness of 6 .mu.m and a
width of 10 mm.
[0197] (5) Next, the plate obtained in the step (4) was grinded
with diamond grindstone, and then a mask was put thereon to make
bottomed holes (diameter: 1.2 mm, and depth: 2.0 mm) for
thermocouples in the surface by blast treatment with SiC or the
like.
[0198] (6) Furthermore, a part of the through holes which would be
conductor filled through holes was hollowed out, and a gold solder
comprising Ni--Au was employed and heated for reflowing at
700.degree. C., so as to connect terminal pins made of koval to the
concave portions.
[0199] Regarding the connection of the terminal pins, a structure,
wherein a support of tungsten supports at three points, is
desirable. This is because the reliability of the connection can be
kept.
[0200] (8) Next, thermocouples for temperature-control were buried
in the bottomed holes and then the holes were sealed with silica
sol (made by Toagosei Co., Ltd., Aron ceramic). The sol was
converted into gel at 120.degree. C. to finish the manufacture of
the ceramic heater.
EXAMPLE 4
Control of the Temperature of a Ceramic Heater
[0201] (1) A temperature-adjusting equipment (made by Omron Corp.,
E5ZE) equipped with a control unit having a power source, a memory
unit, and an operation unit was prepared to connect wirings from
the control unit to the ceramic heater 10 (reference to FIG. 1)
manufactured in Example 1 through the terminal pins 13, and put a
silicon wafer on this ceramic heater 10.
[0202] (2) Next, a voltage was applied to this ceramic heater 10,
and the temperature thereof was once raised to 200.degree. C. The
temperature was further raised up to 200 to 400.degree. C., and
then the temperature was measured with the thermocouples arranged
in the bottomed holes 14a to 14c shown in FIG. 1. The measured
results are shown in FIG. 6. In FIG. 6, the vertical axis
represents temperature and the horizontal axis represents elapsing
time.
[0203] Profiles of electric powers (represented by current values)
supplied to the heating elements 12a, 12b and 12c are shown in FIG.
7. In FIG. 7, the vertical axis represents amperage, and the
horizontal axis represents elapsing time.
[0204] The silicon wafer put on this ceramic heater 10 was not
damaged in the process of the heating, and was uniformly
heated.
EXAMPLE 5
[0205] A ceramic heater was manufactured in the same way as in
Example 1 except that the following points were different.
[0206] That is: first, sheath type thermocouples were used as the
thermocouples. In each of the thermocouples, a K type thermocouple
67 was inserted into a cylinder 66 made of stainless steel and the
surrounding of the thermocouple was filled with MgO power and
alumina powder. As shown in FIG. 4(a), this cylinder 66 was crooked
in a substantially right angle. As shown in FIG. 4(b), the shape of
each bottomed hole 610 was made into a keyhole shape, as viewed
from the above. The structure: wherein a rod shaped body 64 made of
stainless steel was fixed to the tip of a coil spring 65 made of
stainless steel; was adopted. The crooked portion of the cylinder
66 was fixed onto the bottomed holes 610 by pressing the crooked
portion against the bottom surface of the bottomed holes 610 by
means of the rod shaped body 64. The coil spring 65 was attached to
a bottom plate 63 of a supporting case (casing) for a ceramic plate
61.
EXAMPLE 6
[0207] A ceramic heater was manufactured in the same way as in
Example 1 except that the following points were different.
[0208] As shown in FIG. 5, sheath type thermocouples having the
same structure as is in the case of Example 5 were used as the
thermocouples. Moreover, in the same way as in the case of Example
5, the shape of bottomed holes 710 was made into a keyhole shape,
as viewed from the above. The side wall faces thereof were drilled
to make thread grooves. The cylinders 66 having the sheath type
thermocouples were inserted into the bottomed holes 710, and bolts
74 made of stainless steel were screwed in so as to fix the crooked
portions of the cylinders 66 onto the bottomed holes 610 by
pressing the crooked portion against the bottom surface of the
bottomed holes 610.
COMPARATIVE EXAMPLE 1
[0209] A ceramic heater was manufactured in the same way as in
Example 3 except that bottomed holes were formed in such a manner
that the bottom surfaces thereof would be at a level corresponding
to 74% of the thickness of the ceramic plate from the heating
surface thereof, that is, at the same level as the heating element
formed surface, and then the thermocouples were buried in the
bottomed holes to solder the thermocouples with Au--Ni.
COMPARATIVE EXAMPLE 2
[0210] A ceramic heater was manufactured in the same way as in
Example 1 except that the thermocouples were soldered to the
heating element formed surface, that is, the bottom surface, with
Au--Ni.
[0211] Each temperature of the ceramic heaters according to
Examples 1 to 6 and Comparative Examples 1,2 was raised to
200.degree. C. A difference between the highest temperature and the
lowest temperature thereof was measured with a thermoviewer.
[0212] Then, the silicon wafer having a thermocouple with a
temperature of 25.degree. C. was put on the ceramic heater wherein
the temperature thereof was raised to 200.degree. C. A time
(recovery time) until the temperature thereof returned to
200.degree. C., which was the original temperature, was measured.
The results are shown in Table 1.
2 TABLE 1 Temperature-difference Recovery time (.degree. C.)
(seconds) Example 1 0.3 46 Example 2 0.5 50 Example 3 0.4 46
Example 4 0.4 45 Example 5 0.3 47 Example 6 0.3 46 Comparative 2.0
110 Example 1 Comparative 1.3 100 Example 2 Note)
Temperature-difference: temperature-difference between the highest
temperature and the lowest temperature
[0213] In the ceramic substrates of Examples 1 to 6, their
temperature-differences thereof measured with the thermoviewer were
as small as 0.5.degree. C. or lower, and their recovery times until
its recovery to 200.degree. C. were as short as 50 seconds or less.
On the other hand, in Comparative Examples 1,2, their recovery
times and the temperature-differences were large.
INDUSTRIAL APPLICABILITY
[0214] As described above, according to the first and second
aspects of the ceramic heaters of the present invention, the
temperature of an object to be heated can be correctly measured. By
adjusting the state of heating of its heating element on the basis
of the measured result of the temperature, the whole of a silicon
wafer can be uniformly heated.
* * * * *